Why are sponges so important to marine ecosystems?
Francesca Strano
Sponges are the simplest animals on the planet and play vital functions in our oceans.
Sponges are the most ancient animals living on earth.
They populate marine and freshwater ecosystems, and are widespread in tropical, temperate, and polar regions—from coastal areas to the deep sea.
Depending on the species and habitat, sponges can display all the possible colours and shapes you can imagine, and be from just a few millimetres to several square meters in size (pic.1). Some species are seasonal, whereas some deep-sea sponges may live up to 11,000 years. They have a great variety of textures (soft, crumbly, rubbery, or velvety, just to name a few) and they may have peculiar smells, with scents similar to mushroom, mango or garlic. Their bright colours (pic. 2) and incredible smells are the results of the production of chemical molecules that prevent them from being overgrown and predated by other organisms. Interestingly, each sponge species is characterised by a specific set of associated microbes (also called symbionts) living inside their body, that often assist them in the production of chemical compounds and in nutrients absorption.
Sponges love filtering water, and they can pump 72,000 times their body volume per day.
Sponges are not only the oldest, but are also the simplest animals on earth. They don’t have tissues and organs like all other animals; their bodies are simply made up of a few different cell types. Their bodies are supported by a network of flexible proteins (that you may already know if you think about natural sponge for cleaning), together with minuscule pointy structures called spicules. The sponge body is organised in a series of water canals that specialise in water pumping. Sponges respire, feed and reproduce through water pumping. Sponges can asexually reproduce by producing buds or fragmenting themselves, resulting in several clones of the original sponge (pic. 3). They can also reproduce sexually by releasing sperm and eggs, which develop into ciliated swimming larvae after fertilisation (pic. 4). Once they find the right spot to settle, each sponge larvae metamorphose into a new juvenile sponge.
The three main ecological functions of sponges
Sponges are fundamental in all marine ecosystems because they perform a great number of functions to support marine biodiversity and ecosystem functioning:
Reef creation and substrate stabilisation: encrusting sponges stabilise the substrate (sea floor) by glueing coral rubble or pebbles. This allows for the creation of reefs, and assists the colonisation of corals and other habitat-forming species.
Water filtering: sponges trap bacteria, small particles, and dissolved nutrients from water, making them available to other non-filtrating organisms.
Habitat provisioning: with their highly diverse and three-dimensional structures they create shelter for other organisms of all sizes (from bacteria, to small crustaceans, to fish) enhancing biodiversity (pic. 5).
What’s the impact of climate change on sponges?
Marine ecosystems are under threat from the impacts of climate change at all latitudes, with dramatic consequences such as coral bleaching in tropical reefs, sponge mass mortality events in temperate seas, and habitat loss in polar waters. Despite that, the effects of higher temperatures on the physiology and reproduction of temperate sponges are still poorly understood.